JPH06308498A - Ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal element having a large gradation number and high contrast by forming stripes of projections on the surface of one electrode, subjecting the electrode to perpendicular orientation, forming a film on the other electrode, and then uniaxially orienting the film. CONSTITUTION:Stripes of projections 32 are formed on a substrate 31 having an electrode 39 on the one surface. This substrate is stuck with the other electrode substrate 34 by keeping a certain gap by a spacer 33. This element has the electrode 39 where projections 32 are formed and a flat electrode 38, and an oriented film 35 is formed only on the flat side of the element where no projection is formed. This film is uniaxially oriented (by rubbing) in such a manner that the oriented direction is parallel to the longitudinal direction of the stripes of projections on the electrode 39 when the substrates 31, 34 are laminated. On the interface where the stripes of projections are formed, a perpendicularly oriented layer 36 is formed. A ferroelectric liquid crystal 37 is injected between two substrates 31, 34 to obtain the element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device used in televisions and the like, and more particularly to a ferroelectric liquid crystal device using a ferroelectric liquid crystal and having gradation.

[0002]

2. Description of the Related Art In a conventional liquid crystal television panel using an active matrix driving system, thin film transistors (hereinafter referred to as "TFTs") are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TFTs to form a source and drain. The image signal is applied from the source and stored in the capacitor at this time, and the liquid crystal (for example, TN liquid crystal) is driven according to the stored image signal, and at the same time, the voltage of the image signal is modulated. Is used for gradation display.

However, in such an active matrix drive type television panel using a TN liquid crystal, since the TFT used has a complicated structure, the number of manufacturing steps is large and the high manufacturing cost is a bottleneck. In addition to
It is difficult to form a thin film semiconductor (for example, polysilicon or amorphous silicon) forming a TFT over a wide area.

On the other hand, T can be manufactured at low cost.
A passive matrix drive type display panel using N liquid crystal is known. In this display panel, one selection point is provided while scanning one pixel (one frame) as the number of scanning lines (N) increases. The time during which an effective electric field is applied (duty ratio) decreases at a rate of 1 / N, which causes crosstalk, and has the problem that the contrast of the image is low. Is difficult to control the gradation of each pixel by voltage modulation, and therefore it is not suitable for a display panel having a high number of wirings, particularly a liquid crystal television panel.

As a solution to such a fundamental problem of the conventional TN liquid crystal, a ferroelectric liquid crystal device having a bistable state has been proposed in US Pat. No. 4,367,924 to Clark and Lagavar et al. . It has been considered that this ferroelectric liquid crystal element is not suitable for gradation expression because it ideally tries to stabilize in one of two bistable states and does not take an intermediate molecular position. Therefore, in order to perform gradation display using the ferroelectric liquid crystal element, it was necessary to rely on gradation display by a digital method typified by a pixel division method.

[0006]

However, in the gradation display method by the digital method described above, one frame is divided into subclaims composed of a plurality of pixels, and when drawing one frame, The pixels are driven by applying electric fields having different duty ratios. In this case, in order to obtain high gradation characteristics,
As the number of pixels that make up one subclaim increases,
As the display screen becomes larger, the duty ratio per pixel becomes considerably smaller. Therefore, in order to obtain high contrast, high-speed response of the liquid crystal material is required. Further, a large number of drive electrodes are required for gradation display of one pixel. Further, there are too many technical problems to be solved for use in a high gradation display device such as a high definition television (HDTV) which has been attracting attention in recent years because it requires a complicated arithmetic processing circuit.

On the other hand, the present inventors firstly proposed a method of applying gray scale display by applying pulse voltages having different peak values corresponding to gray scale display to a liquid crystal for a single frame. I found it. However, in this method, since the threshold characteristic of the ferroelectric liquid crystal is steep, the applied voltage must be controlled with extremely high accuracy. Moreover, the position of the domain-inverted region (domain) that locally develops in the display pixel with respect to the applied voltage and the growth direction thereof are likely to be random,
As a result, it was difficult to easily obtain a linear applied voltage-transmittance characteristic.

Further, there is room for further improvement in terms of contrast.

[0009]

The present invention has been made in view of the above problems, and an object of the present invention is to provide a ferroelectric liquid crystal element having a large number of gradations with a simple structure.

Another object of the present invention is to provide a liquid crystal device having high contrast.

The above object can be achieved by the following configurations.

That is, according to the present invention, in a liquid crystal display device having a ferroelectric liquid crystal disposed between a pair of counter electrodes, stripe-shaped protrusions are formed on one electrode surface of the counter electrodes, and the protrusions are formed. An alignment film is formed on the formed electrode, and uniaxial alignment treatment is performed so that the alignment direction of liquid crystal molecules at the interface is substantially parallel to the substrate. Is a ferroelectric liquid crystal element characterized by being subjected to vertical alignment treatment.

The above object is also achieved by the following constitution.

That is, according to the present invention, in a liquid crystal display device having a ferroelectric liquid crystal disposed between a pair of counter electrodes, stripe-shaped protrusions are formed on one electrode surface of the counter electrodes, and the protrusions are formed. A vertical alignment treatment is performed on the formed electrode, an alignment film is formed on the other electrode of the counter electrode, and the alignment direction of liquid crystal molecules at the interface is substantially parallel to the substrate. The ferroelectric liquid crystal element is characterized by being subjected to such uniaxial alignment treatment.

Further, in a liquid crystal display device having a ferroelectric liquid crystal disposed between a pair of counter electrodes, a stripe-shaped convex portion is formed on one surface of the counter electrode, and the counter electrode is formed. A ferroelectric liquid crystal device in which only one of the surfaces is subjected to vertical alignment treatment.

[0016]

According to the present invention, it is possible to display a high-contrast image.

Further, according to the present invention, since the size and density of the domain respond well to the applied voltage with good reproducibility, a linear applied voltage-transmittance characteristic can be easily and stably obtained. Excellent analog gradation display can be performed.

Further, according to the present invention, a domain which responds favorably to an applied voltage is formed only by a combination of a reliable technique of substantially setting the alignment state of liquid crystal and forming an uneven stripe. Therefore, it is possible to perform analog gradation display with good controllability.

Then, a vertical alignment treatment is applied to the convex electrode side to obtain a good alignment state. On the other hand, by performing the vertical alignment treatment on the electrode side having no convex portion, it is possible to display a larger number of gradations.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention is shown in FIGS.

The device of FIG. 1 has a form in which a vertical alignment treatment layer 36 is provided on the side where the stripe-shaped convex portions 32 are provided.

On the other hand, the element shown in FIG. 2 has a stripe-shaped convex portion 32.
This is a mode in which the vertical alignment treatment layer 36 is provided on the side where there is no edge.

In either form, high contrast display can be performed. The details will be described above.

On the other hand, in the device of FIG. 1, the electrode 3 on one side is
Stripe-shaped irregularity modification 32 on the side of the substrate 31 having 9
Are formed and are bonded to the counter electrode substrate 34 with a constant gap maintained by the spacer 33. The alignment film 35 is formed only on the flat side which is not modified, of the electrode side which is provided with the unevenness modification 32 and the flat electrode side which is not modified, and when the upper and lower substrates are bonded together. Is subjected to a uniaxial alignment treatment (rubbing) in a direction parallel to the longitudinal direction of the stripes of the stripe-shaped irregularities on the counter electrode, and a vertical alignment layer is formed on the interface on the opposite side where the stripe-shaped irregularities are formed. 36 is formed. A ferroelectric liquid crystal 37 is injected between the two substrates to form an element.

A cross-sectional view of the device of the present invention is shown in FIG. A convex portion 32 as an irregularity modification is formed on the side of the substrate 31 having the electrode 39 on one side, and the convex portion 32 is bonded to the counter electrode substrate 34 with a constant gap maintained by a spacer 33. An alignment film 35 is formed on the side of the electrode on which the irregularity modification 32 is applied and on the side of the flat electrode that is not modified on the irregularity modification, and the uniaxial alignment treatment (rubbing) is performed along the longitudinal direction of the stripe. The vertical alignment treatment layer 36 is applied to the interface on the flat side. A ferroelectric liquid crystal 37 is injected between the two substrates to form an element.

At least one of the pair of electrodes forming the liquid crystal cell, that is, the pixel, used in the present invention is preferably formed of a transparent conductor. Examples of such a material include tin oxide, indium oxide, and indium oxide. Tin (IT
O) and the like are preferably used.

The alignment film used is preferably an organic substance such as polyimide or polyvinyl alcohol, and the vertical alignment treatment is preferably polysiloxane coating or silane coupling treatment, but is not limited thereto.

The ferroelectric liquid crystal preferably used in the present invention has a large cone angle of liquid crystal molecules of 20 ° or more in the smectic C layer, and one electrode interface is subjected to horizontal alignment treatment and the other electrode interface is subjected to horizontal alignment treatment. Shows a good orientation in an asymmetric cell where vertical alignment treatment is applied, and makes the angle formed by two extinction positions close to twice the cone angle of the molecule in the chiral smectic C phase. As a result, a good liquid crystal element having high contrast can be obtained.

In the present invention, the stripe-shaped convex portions may be formed in one pixel in a uniform shape or in a non-uniform shape. Alternatively, one pixel may be divided into a plurality of sub-pixels, and the sub-pixels may be uniform and different sub-pixels may not be uniform. Such a stripe-shaped convex portion may be formed by using a part of the electrode or the alignment film thereon, or a special member for the stripe-shaped convex portion may be provided. In any case, the stripe-shaped convex portion can be easily formed by film formation and patterning.

It is necessary to select an optimum value for the pitch of the stripe convex portions depending on the liquid crystal material used and the cell thickness, but it is generally preferable to be 3 μm to 50 μm. In addition, the smaller the width of the concave portion and the convex portion is about the cell thickness or more, generally 1 μm.
The above is preferable. Further, the length of the stripe is preferably about a chiral pitch or more, and generally, it is necessary to be 3 times or more, and preferably 10 times or more, to the smaller width of the concave portion and the convex portion. It is sufficient that the unevenness has a level difference that maintains a uniform alignment state, and is about half the cell thickness or less,
Generally, the range of 100 nm to 500 nm is preferable.

The liquid crystal element of the present invention is preferably used as an element for displaying a gray scale.

In FIG. 3, the liquid crystal molecules are polarization-inverted to the other of the bistable states in a region (black region) 12 in the initial state, which is one of the bistable states. Pixels 11 in which a plurality of domains (white regions) 13 formed in a striped pattern are schematically shown. On the other hand, FIG. 4 shows, as a comparison target, a pixel 21 in which domains 22 are not formed in a striped pattern but are formed randomly. When the domains 13 are expressed in stripes, the probability that the same domain appears when signals of the same waveform are applied becomes extremely high. Moreover, the length and density of the striped domains change linearly according to the peak value and / or pulse width of the signal. Therefore, the controllability of the transmittance is improved and the display is suitable for gradation display. on the other hand,
In the case of FIG. 4, even if signals of the same waveform are applied,
The shape and size of the domains appearing each time are often different, resulting in poor reproducibility. Therefore, the transmittance does not completely correspond to the peak value and / or the pulse width of the signal.

The halftone signals used in the present invention include:
It may be either a signal in which only the peak value is modulated, a signal in which only the pulse width is modulated, or a signal in which both the peak value and the pulse width are modulated. The halftone signal generating means for generating such a halftone signal is manufactured by a semiconductor integrated circuit or the like. More preferably, it is desirable to apply an independent signal to each of the pair of electrodes and combine them to obtain a halftone signal.

Then, the liquid crystal material, the electrode material, the alignment state in the liquid crystal cell, etc. are appropriately selected and designed, and the region in which the polarization is inverted in accordance with the halftone signal is a stripe shape substantially parallel to the layer direction of the ferroelectric liquid crystal. It is preferably expressed as a region. Such a striped domain can be more easily expressed by using striped unevenness.

FIG. 5 is a schematic view for explaining a state of a domain when one pixel of the device of the present invention is observed from a direction perpendicular to the surface. 41 is a pixel, 42 is a stripe convex portion,
43 is an inversion domain. The inversion domain 43 is formed in a striped pattern, and any domain in FIG. 4 has a layer normal direction L.
It almost coincides with the vertical direction. That is, the inversion domain 43 extends in the layer direction. Such a striped domain extends across a plurality of stripes as in (A) and only in the striped recess as shown in (B) is clearly striped in the same direction, connecting the striped recesses in a ladder shape. There are cases of shape. It is possible to preferentially produce the state (A) by providing stripe unevenness of the same pitch and narrowing the width of the convex portion, for example, by forming the convex portion having a width of ½ or less of the chiral pitch of the liquid crystal. Alternatively, it is possible to preferentially create the state (A) by providing stripe unevenness having the same pitch and making the stripe step relatively low. In both cases (A) and (B), the number of inversion domains changes depending on the applied signal while the number of stripes changes. Moreover, the instability in which the domain expands or contracts further after the domain wall is formed after the signal application is extremely small, and variations in transmittance between pixels are hardly seen. As described above, in the case of a cell without stripes, the inversion domain does not have a clear directionality and has no regular appearance position as shown in FIG. 4, and the transmittance varies between pixels. Instability of the domain will be seen after the domain wall is formed.

Further, in order to improve the gradation display characteristic, it is preferable to change the pitch of the unevenness within the unit pixel.

The area of the inversion domain after applying the same voltage is larger as the stripe pitch is smaller, and the density of the stripe domain formed is smaller as the pitch is larger. It is considered that the cause of this is that the dynamic correlation between stripes in the transient state greatly differs depending on the stripe interval. That is, after a similar transient state, when the stripe pitch is small, the striped domain remains as a latch domain, but when the stripe pit is large, the inversion domain does not remain as in the case where the pitch is small. It means that it will be returned to the state.

That is, it can be considered that the difference in the mechanical correlation in the transient state occurs due to the interval between the stripe-shaped convex portions, which causes the threshold difference.

Therefore, the threshold value can be satisfactorily controlled by changing the pitch of the stripe-shaped convex portions within one pixel. A state of domain inversion when the pitch of the stripe-shaped convex portions in one pixel is changed is schematically shown in FIG. In each pixel in FIG. 6, the pitch of the stripe-shaped convex portions continuously increases from the left side to the right side. The inversion domain appears from a region where the stripe-shaped convex portions have a narrow interval, and a clear threshold gradient is formed in the pixel.

According to the embodiment shown in FIG. 1 of the present invention, a concavo-convex stripe is provided only on the surface of one electrode, and the electrode on the side where the concavo-convex stripe is formed is subjected to vertical alignment treatment to provide the concavo-convex stripe. The alignment film is formed only on the opposite electrode side, which is not aligned, and the uniaxial alignment treatment is performed to control the shape of the domain-inverted domains of the liquid crystal molecules so as to have a striped shape, and to improve the gradation controllability as well. It forms an alignment state.

The element of the present invention in which the alignment film is formed only on the electrode side where the stripe-shaped protrusions are not formed and subjected to the uniaxial alignment treatment, and the counter electrode side where the stripe-shaped protrusions are formed is subjected to the vertical alignment treatment, , On the contrary, when an alignment film is formed on the electrode of the substrate with the irregularity modification and subjected to uniaxial orientation treatment, and is injected into the cell with the vertical orientation treatment on the side without the irregularity modification. In comparison, the disorder of the orientation due to the unevenness was remarkably small, and a better orientation could be obtained.

Further, in the cell in which the alignment films are formed on both sides and the uniaxial alignment treatment is applied on both sides, as in this case,
It is difficult to align a liquid crystal material having a cone angle of liquid crystal molecules of 20 ° or more in the smectic C phase to form a high-contrast device and perform switching.

Further, the device of FIG. 1 is obtained by forming alignment films on the substrates on both sides with and without ruggedness modification, performing uniaxial alignment treatment on both sides, and injecting a liquid crystal having a small cone angle. Compared with the above, the disorder of the orientation due to the unevenness was small, and the improvement of the characteristics beyond the improvement of the contrast was observed. This is unavoidable when the alignment film formed on the irregularity is rubbed. It is considered that it is difficult for the element of FIG. 2 to have the difference in the rubbing strength between the concave portion and the convex portion, the peculiarity of rubbing on the side surface of the convex portion, and the like.

Therefore, when the orientation of the liquid crystal is the maximum point of device design, the device form shown in FIG. 1 is preferably used. Specifically, it is suitable for manufacturing a low-cost element that does not have high function.

On the other hand, the element of the form shown in FIG.
It is most suitable for use as a high-performance display device with more gradation. However, in this case, the compatibility with the liquid crystal material should be sufficiently considered so that the alignment is as good as possible.

According to the embodiment shown in FIG. 2 of the present invention, the uneven stripes are provided only on the surface of one electrode, and the alignment film is formed only on the side where the uneven stripes are formed to perform the uniaxial alignment treatment. By subjecting the counter electrode on which the uneven stripe is not formed to the vertical alignment treatment, the shape of the domain inversion domain of the liquid crystal molecules is controlled to be a stripe shape,
In addition, it is possible to improve gradation controllability and perform display with more gradations.

On the other hand, in the element in which the alignment film is formed on the side where the stripe-shaped convex portions are formed, the uniaxial alignment treatment is performed, and the vertical alignment treatment is performed on the counter electrode side, the one having no irregularity modification is formed. An alignment film is formed on the substrate and uniaxial alignment treatment is applied,
It is an index showing the gradation controllability, as compared with the case where it is injected into a cell which has been subjected to vertical alignment treatment on the side with the irregularity modification.
The value of γ = (saturation inversion voltage) / (inversion threshold voltage) can be increased, and the controllability of gradation display can be improved. The applied voltage-transmittance characteristic of this device is shown in FIG. 7A. An alignment film was formed on the interface without the irregularity modification, and uniaxial alignment treatment was performed to make it perpendicular to the interface with the irregularity modification. The voltage-transmittance characteristic of the element subjected to the alignment treatment is shown in FIG. 7B, and the voltage-transmittance characteristic of the element in which the stripe-shaped convex portions are not modified is shown in FIG. 7C.
It is apparent that the element of the form of the present invention has the highest gradation controllability.

Further, an alignment film is formed on the substrates on both sides with and without the irregularity modification, and uniaxial alignment treatment is performed on both sides.
When compared with the characteristics of an element obtained by injecting a liquid crystal having a smaller cone angle than that used in the present invention, the element of the present invention is an index showing not only high contrast but also gradation controllability, The value of γ = (saturation inversion voltage) / (inversion threshold voltage) was further increased, and the tone controllability was excellent. This is because in the case of the configuration of FIG. 2, where the distribution of the alignment regulating force formed by rubbing the uneven surface creates a change in the threshold value to some extent, and the change does not have the alignment regulating force of the counter substrate. It is thought that this is because it appears more markedly.

[0049]

【Example】

(Embodiment 1) FIG. 8 shows a pixel pattern of the liquid crystal display element of this embodiment. The square portion of 61 indicates each pixel, and 6
Reference numeral 2 denotes a stripe convex portion provided on the transparent thin film electrode on the substrate. The size of the pixel 61 is 200 μm on a side, the width of the stripe convex portion is 3 μm, and the space is 5 μm. FIG. 9 shows a cross section of the cell along the line aa 'in FIG. ITOs 73 and 74 have a thickness of 150 n on the glass substrates 71 and 72.
The film is formed in about m, and the pixel pattern and the stripe pattern are formed by two photolithography steps. Reference numeral 75 denotes a stripe convex portion, and the step of the stripe pattern is about 70 nm. Furthermore, polysiloxane 77 is spin-coated thereon. On the other hand, on the surface of the electrode on which the stripe convex portion is not formed, polyimide 76 is formed into a film having a thickness of about 20 nm and subjected to rubbing treatment. The rubbing direction is a direction in which the upper and lower substrates are parallel to the longitudinal direction of the stripes of the uneven stripe modification on the counter electrode when the substrates are bonded to each other. After that, the two substrates are bonded together with a cell gap of 1.2 μm. Ferroelectric liquid crystal is injected into the gap. As a ferroelectric liquid crystal,

[0050]

[Outer 1] And a tilt angle of liquid crystal molecules at 30 ° C. of 25.3 ° C. was used.

A liquid crystal cell was prepared as described above. This cell showed a very good orientation, and there was almost no disorder in the orientation at the convex portion.

A uniaxial alignment treatment is performed by forming an alignment film on the surface of the element of the present invention, the element not subjected to the stripe-shaped irregularity modification, and the electrode surface on which the irregularity modification is formed, which is the opposite of the present invention. The same liquid crystal material was injected into three types of devices, in which the electrode surface of (1) was subjected to vertical alignment treatment, and the orientation was evaluated. The orientation was evaluated based on the transmittance T ₀ measured at the extinction position when the transmittance was 100% when the upper and lower polarizing plates were in the para-Nicol state, and when returning to crossed Nicols again. The three types of cells have the same manufacturing method, liquid crystal material, alignment film, vertical alignment treatment, cell gap, and the like. Table 1 shows T ₀ measured with the three types of devices.

[0053]

[Table 1]

[0054] From this table, T ₀ value of the element of the present invention, will be apparent that T ₀ value of the element that does not form any unevenness to be approximately the same, this is, the device of the present invention, uneven It is clearly shown that there is almost no disorder in the orientation due to the formation of the.

In the device obtained in this example, the angle formed by the two extinction positions was 41.6 ° at 30 ° C., which was a value close to twice the tilt angle of the liquid crystal molecules, and high contrast could be achieved. . The layer normal direction in the smectic C phase was substantially parallel to the longitudinal direction of the stripe pattern.

A pulse voltage as shown in FIG. 10 was applied between the upper and lower electrodes of this cell, and the optical response characteristics were measured. In this embodiment, Δt = 20 μsec and V _ap = 15 to 30 V. Hereinafter, this applied voltage waveform was used for optical characteristic evaluation.

In a 4 × 4 matrix, different pulse voltages V _ap were applied in the initial black state and the inverted domain shape was observed. As a result, a striped domain as schematically shown in FIG. 5A was observed. It was confirmed that the width of the stripe widens as the applied voltage increases.

The applied voltage-transmittance characteristic of this element was very stable and excellent in reproducibility, and the variation in the transmittance of each pixel was very small.

Further, γ = which is an index showing gradation controllability
The value of (saturation inversion voltage) / (inversion threshold voltage) was increased from γ = 1.03 in the element in which the stripe-shaped convex portion was not formed to γ = 1.07 to improve the gradation controllability. I was able to.

(Embodiment 2) FIG. 11 shows a pixel pattern of the liquid crystal display element of this embodiment. A square portion of 91 indicates each pixel, and 92 is a stripe convex portion provided on the transparent thin film electrode on the substrate. The size of the pixel 91 is 2 on each side.
00 μm, and the width of the stripe convex portion is 3 μm. The densest part of the stripe-shaped convex part is a 1 μm space, the sparsest part is a 15 μm space, and the step is 70 nm. The rubbing direction is the same as that in Example 1, and is a direction parallel to the longitudinal direction of the stripes of the uneven stripe modification on the counter electrode when the upper and lower substrates are bonded together. The cell manufacturing method, the liquid crystal material, the alignment film, the vertical alignment treatment, the cell gap and the like are the same as in the first embodiment.

A liquid crystal cell was prepared as described above. This cell showed a very good orientation, and there was almost no disorder in the orientation at the convex portion. The measured T ₀ value is 0.6,
It was the same as in Example 1.

In the device obtained in this example, the angle formed by the two extinction positions was 41.2 ° at 30 ° C., which was a value close to twice the tilt angle of the liquid crystal molecules, and high contrast could be achieved. . The layer normal direction in the smectic C phase was substantially parallel to the longitudinal direction of the stripe pattern.

The optical response characteristics of this cell were measured under the same conditions as in Example 1.

When a different pulse voltage V _ap was applied in the initial black state in a 4 × 4 matrix and the inverted domain shape was observed, as shown schematically in FIG. 6, when the applied voltage was low, stripes were formed. It was confirmed that the striped domains appeared only on the side with a small interval and extended to the side with a wider stripe interval with the increase of the applied voltage.

The applied voltage-transmittance characteristic of this element was very stable and excellent in reproducibility, and the variation in the transmittance of each pixel was very small.

The applied voltage-transmittance characteristic of this element is shown in FIG.
Shown in. (A) is the characteristic observed in the cell of the present embodiment, and (B) is the characteristic observed in the cell without the irregularity modification. The value of γ = (saturation inversion voltage) / (inversion threshold voltage), which is an index showing the gradation controllability, was γ = 1.03 in the element in which the stripe-shaped convex portion was not formed, but γ = 1.14. As a result, the gradation controllability could be improved very effectively by changing the stripe interval within the pixel.

As described above, according to Examples 1 and 2, in the high-contrast ferroelectric liquid crystal element, the reproducibility of halftone display can be kept good and the gradation controllability can be greatly improved. Therefore, it is possible to perform halftone display with a high gradation number. Moreover, it is possible to perform a halftone display in which the alignment state is extremely good and the reproducibility is high.

(Embodiment 3) FIG. 13 shows a pixel pattern of the liquid crystal display element of this embodiment. A square portion 71 indicates each pixel, and 72 is a stripe convex portion provided on the transparent thin film electrode on the substrate. The size of the pixel 71 is 2 on each side.
00 μm, stripe convex width 3 μm, space 5
μm. FIG. 14 shows a cross section of the cell along the line aa 'in FIG. ITO83 on the glass substrate 81, 82,
84 is formed with a thickness of about 150 nm, and a pixel pattern and a stripe pattern are formed by two photolithography steps. Reference numeral 85 is a stripe convex portion, and the step of the stripe pattern is about 70 nm. Further, a polyimide 87 having a thickness of about 20 nm is formed thereon and a rubbing process is performed. The rubbing direction is parallel to the longitudinal direction of the stripe. On the other hand, polysiloxane 86 is formed on the electrode surface on the side where the stripe protrusions are not formed.
Is spin coated. After that, the two substrates are bonded together with a cell gap of 1.2 μm. Ferroelectric liquid crystal is injected into the gap. As a ferroelectric liquid crystal,

[0069]

[Outside 2] And a tilt angle of liquid crystal molecules at 30 ° C. of 25.3 ° C. was used.

A liquid crystal cell was prepared as described above. This cell shows a good orientation, and the angle formed by the two extinction positions is 41.0 ° at 30 ° C., which is 2 ° of the tilt angle of the liquid crystal molecules.
It was a value close to twice, and high contrast could be achieved. The layer normal direction in the smectic C phase was substantially parallel to the longitudinal direction of the stripe pattern.

A pulse voltage as shown in FIG. 10 was applied between the upper and lower electrodes of this cell, and the optical response characteristics were measured. In this embodiment, Δt = 20 μsec and V _ap = 15 to 30 V. Hereinafter, this applied voltage waveform was used for optical characteristic evaluation.

When a different pulse voltage V _ap was applied in the initial black state in a 4 × 4 matrix to observe the inversion domain shape, a striped domain as schematically shown in FIG. 5A was observed. It was confirmed that the width of the stripe widens as the applied voltage increases.

The applied voltage-transmittance characteristic of this element was very stable and excellent in reproducibility, and the variation in transmittance of each pixel was very small.

Further, γ = which is an index showing the gradation controllability
The value of (saturation inversion voltage) / (inversion threshold voltage) was increased from γ = 1.03 in the element in which the stripe-shaped convex portion was not formed to γ = 1.10 to improve the gradation controllability. I was able to.

(Embodiment 4) FIG. 15 shows a pixel pattern of the liquid crystal display element of this embodiment. A square portion of 1001 indicates each pixel, and 1002 is a stripe convex portion provided on the transparent thin film electrode on the substrate. The size of the pixel 1001 is 200 μm on a side, and the width of the stripe convex portion is 3 μm. The densest part of the stripe-shaped convex part is a 1 μm space, the sparsest part is a 15 μm space, and the step is 7
It is 0 nm. The rubbing direction is parallel to the longitudinal direction of the same stripe as in Example 3, and the manufacturing method, liquid crystal material, alignment film, vertical alignment treatment, cell gap, etc. are the same as in Example 3.

A liquid crystal cell was prepared as described above. This cell shows a good orientation, and the angle formed by the two extinction positions is 41.4 ° at 30 ° C., which is 2 ° of the tilt angle of the liquid crystal molecules.
It was a value close to twice, and high contrast could be achieved. The layer normal direction in the smectic C phase was substantially parallel to the longitudinal direction of the stripe pattern.

The optical response characteristics of this cell were measured under the same conditions as in Example 3.

In a 4 × 4 matrix, different pulse voltages V _ap were applied in the initial black state, and the inversion domain shape was observed. As shown schematically in FIG. 6, when the applied voltage is low, stripes are formed. It was confirmed that the striped domains appeared only on the side with a small interval and extended to the side with a wider stripe interval with the increase of the applied voltage.

The applied voltage-transmittance characteristic of this element was very stable and excellent in reproducibility, and the variation in transmittance between pixels was very small.

The applied voltage-transmittance characteristic of this element is shown in FIG.
Shown in. (A) is the characteristic observed in the cell of the present embodiment, and (B) is the characteristic observed in the cell without the irregularity modification. The value of γ = (saturation inversion voltage) / (inversion threshold voltage), which is an index showing the gradation controllability, was γ = 1.03 in the element in which the stripe-shaped convex portion was not formed, but γ = 1.20. As a result, the gradation controllability could be improved very effectively by changing the stripe interval within the pixel.

As described above, according to Examples 3 and 4, in the high contrast ferroelectric liquid crystal element, the reproducibility of halftone display is kept good and the gradation controllability is further improved. Therefore, it is possible to perform halftone display with a higher number of gradations.

[0082]

According to the present invention, it is possible to provide a liquid crystal element having a high contrast and capable of performing excellent halftone display.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a liquid crystal element according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a liquid crystal element according to another embodiment of the present invention.

FIG. 3 is a schematic plan view illustrating a striped domain.

FIG. 4 is a schematic plan view illustrating a random domain.

FIG. 5 is a plan view illustrating a stripe domain observed in a cell provided with a stripe convex portion.

FIG. 6 is a plan view illustrating formation of an inversion domain in a cell in which the interval between stripe-shaped convex portions is changed within a pixel.

FIG. 7 is a diagram showing applied voltage-transmittance characteristics of the device of the present invention.

8 is a diagram showing a stripe pattern of the device of Example 1. FIG.

9 is a cross-sectional view of the device of Example 1. FIG.

FIG. 10 is a diagram showing a drive applied voltage.

FIG. 11 is a diagram showing a stripe pattern of the device of Example 2;

FIG. 12 is a diagram showing applied voltage-transmittance characteristics of the device of Example 2;

FIG. 13 is a diagram showing a stripe pattern of an element of Example 3;

FIG. 14 is a cross-sectional view of an element of Example 3.

FIG. 15 is a diagram showing a stripe pattern of an element of Example 4;

16 is a diagram showing an applied voltage-transmittance characteristic of the device of Example 4. FIG.

[Explanation of symbols]

 31 ITO on the upper substrate 32 Striped convex portion 33 Spacer 34 ITO on the lower substrate 35 Alignment film 36 Vertical alignment layer 37 Ferroelectric liquid crystal 38 Electrode 39 Electrode 41 Pixel area 42 Stripe convex 43 Inversion domain 51 Pixel area 52 Inversion Domain 61 Pixel area 62 Stripe convex portion 71, 72 Glass substrate 73, 74 ITO 75 Stripe convex portion 76 Polyimide 77 Vertical alignment treatment layer 91 Pixel area 92 Stripe convex portion

Claims (9)

[Claims] 1. A liquid crystal display device having a ferroelectric liquid crystal disposed between a pair of counter electrodes, wherein an electrode in which a stripe-shaped convex portion is formed on one electrode surface of the counter electrode and the convex portion is formed. An alignment film is formed on the top surface, and uniaxial alignment processing is performed so that the alignment direction of liquid crystal molecules at the interface is substantially parallel to the substrate. Vertical alignment processing is performed on the other electrode of the counter electrode. Ferroelectric liquid crystal element characterized by being provided with. 2. The uniaxial orientation treatment direction is substantially parallel to the longitudinal direction of the stripe-shaped protrusions.
A ferroelectric liquid crystal device according to item 1. 3. The ferroelectric liquid crystal device according to claim 1, wherein the pitch of the stripe-shaped convex portions is uniform within the pixel. 4. The ferroelectric liquid crystal device according to claim 1, wherein the pitch of the stripe-shaped convex portions is non-uniform within the pixel. 5. A liquid crystal display device having a ferroelectric liquid crystal disposed between a pair of counter electrodes, wherein an electrode in which a stripe-shaped convex portion is formed on one electrode surface of the counter electrode and the convex portion is formed. Vertical alignment treatment is performed on the upper surface, an alignment film is formed on the other electrode of the counter electrode, and uniaxial alignment in which the alignment fragrance of liquid crystal molecules at the interface is substantially parallel to the substrate. A ferroelectric liquid crystal device characterized by being treated. 6. The direction of the uniaxial alignment treatment is substantially parallel to the longitudinal direction of the stripe-shaped protrusions.
A ferroelectric liquid crystal device according to item 1. 7. The ferroelectric liquid crystal device according to claim 5, wherein the pitch of the stripe-shaped convex portions is uniform in the pixel. 8. The ferroelectric liquid crystal element according to claim 5, wherein the pitch of the stripe-shaped convex portions is non-uniform within the pixel. 9. A liquid crystal display device having a ferroelectric liquid crystal disposed between a pair of counter electrodes, wherein a stripe-shaped convex portion is formed on one surface of the counter electrode, and the counter electrode of the counter electrode is formed. A ferroelectric liquid crystal device characterized in that only one surface thereof is subjected to vertical alignment treatment.